1. Field of the Invention
The present invention relates to an overheat detection circuit configured to detect an abnormal temperature of a semiconductor device.
2. Description of the Related Art
A circuit disclosed in Japanese Patent Application Laid-open No. Hei 6-242176 has been known as a related-art overheat detection circuit.
FIG. 3 is a circuit diagram of the related-art overheat detection circuit. The related-art overheat detection circuit includes a reference voltage section 10, a temperature sensor 20, and a comparator 30. The related-art overheat detection circuit controls the comparator 30 to compare and determine a voltage generated at a PN junction element 21, being a temperature sensitive element, and a reference voltage Vref output from a reference voltage circuit 11, to thereby detect an overheated state. The voltage generated at the PN junction element 21 basically exhibits negative temperature characteristics as long as the PN junction element 21 is biased by a constant current of the constant current circuit 22. When an ambient temperature increases and the voltage generated at the PN junction element 21 falls below the reference voltage Vref, the comparator 30 outputs a signal indicating the overheated state.
However, in the above-mentioned overheat detection circuit, for example, in a case where the constant current circuit 22 includes a current mirror circuit formed of PMOS transistors, a leakage current between a drain terminal of the PMOS transistor and a substrate is increased when the temperature becomes higher, which leads to an increase in constant current biasing the PN junction element 21. Therefore, there is a problem in that the voltage of the PN junction element 21 is increased and the temperature can thus not be accurately detected.
Moreover, for example, in a case where the reference voltage circuit 11 includes a saturation-connected NMOS transistor, a leakage current between a drain terminal of the NMOS transistor and a substrate is increased when the temperature becomes higher, which leads to a decrease in reference voltage Vref of the reference voltage circuit 11. Consequently, there is a problem in that a reference of the comparator 30 varies and the temperature can thus not be accurately detected.
Moreover, for example, a leakage current of a transistor forming the comparator 30 is increased to adversely affect an internal operating point, which leads to a problem in that neither of the detection of the temperature nor the output of the detection result can be accurately performed.